HYVAN ANAESTHESIA LIMITED WAS REQUESTED TO MODIFY THE HYVAN ANAESTHESIA MACHINE TO FUNCTION AS A BACK-UP VENTILATOR SUITABLE FOR VENTILATING COVID-19 PATIENTS SHOULD NO ICU VENTILATORS BE AVAILABLE.
Minimal changes to the machine were required. The major change was converting to a high volume flow WITHOUT RECIRCULATIONand the removal of the soda lime canister and vaporizer.
Diagram: Working concept of the Hyvan Covid ventilator: The 'circle' anaesthesia machine has been converted to a high flow machine (ie patients minute volume +) and the expired gas is vented to atmosphere via a viral filter and variable PEEP valve. The patient connection is light weight and a sampling port allows measurement of CO2 etc.
The above diagram is reflected in the two photos below. For convenience the humidifier and water trap have been omitted in the photos.
The above photo shows the patient circuit set up.
Note the red expiratory port is plugged so that all the gas flow from the machine comes from the green inspiratory port.
Note the viral filter and the brown mushroom valve. This valve is autoclavable. The yellow hose pressurises the balloon in the mushroom valve at the start of inspiration (thus blocking the expiratory limb and allowing the lungs to inflate). The expiratory gas is vented to atmosphere via a variable PEEP valve.
The above photo shows the same set up except the mushroom valve assembly is hung on the plugged expiratory port.
IT IS IMPORTANT TO NOTE THAT THE EXPIRED GAS DOES NOT RETURN TO THE MACHINE. IT IS VENTED TO ATMOSPHERE VIA THE PEEP VALVE
Note also the sodalime canister has been removed and sealed with a plate.
In the above photo, note the presence of a one way valve at outlet to allow patient to draw room air if necessary and the presence of a humidifier.
When using the Hyvan Covid ventilator, a high fresh gas flow must be used. This must be at least the patient minute volume and in practice a fresh gas flow of at least 8 litres/minute is required.
The Respiratory rate is set and an I:E ratio chosen. The tidal volume is then set. A spirometer can be added to the circuit to measure the exact tidal volume but measuring the tidal volume by watching the bellows excursion is usually adequate. The PEEP value can be adjusted (up to 25 cm water). The fresh gas flow must be sufficient to raise the bellows to the top of the canister prior to inspiration.
The patient is free to take a spontaneous breath at any stage. The breath will be drawn direct from the bellows.
The two ventilator modes are VOLUME CONTROL and PRESSURE CONTROL. There is no trigger, SIMV or PSV mode.
ALARMS: High and Low pressure, oxygen failure and negative pressure. Should the charger be disconnected, the battery alarm will flash and sound. This can be cancelled by two rapid presses of the mute button. If the ventilator is turned off (eg during patient suctioning) an alarm will sound. This can be cancelled by turning the ventilator back on or two quick presses on the mute button.
In early March 2020 the Covid-19 pandemic swept through Italy and Spain. The ICUs were overwhelmed and there were insufficient ventilators for the patients requiring them. The New Zealand Government was alarmed and made urgent plans prepare for Covid-19 reaching NZ. ICU ventilators were in demand around the world and Hyvan Anaesthesia Limited was asked to modify our anaesthetic machine to act as a back up ventilator in case NZ ran out of ICU ventilators.
We are manufacturing 50 Hyvan Covid ventilators and these will be ready by the end of April 2020. At this stage (mid April) NZ appears to have the Covid 19 threat under control and it is unlikely the Hyvan Covid ventilaotrs will be required in NZ. They will be available to overseas purchasers at a cost of USD 10,500. Hyvan Anaesthesia is an ISO 13485 certified company. We will soon have the CE mark and TGA.
When the pandemic is over, these ventilators can be returned to Hyvan Anaesthesia Limited for conversion back to Hyvan anaesthesia machines.